The present invention relates to a synchronization system and a communication device. This invention can be applied to a synchronization system in which, for example, a plurality of communication devices exchange time synchronization messages to which a security process has been applied via a network to establish time synchronization among the plurality of communication devices.
In order to establish secure and precise time synchronization, it is desirable to assign time information acquired in a physical layer to a time synchronization message immediately before transmission of the time synchronization message and then apply a security process of, for example, an authentication code, a digital signature, or the like to the time synchronization message.
However, since a delay time (e.g., a time required for the security process) taken due to the application of the security process to the time synchronization message is needed, there is a problem of the difference corresponding to the delay time required for the security process arising between a time at which the transmission of the time synchronization message is actually performed and a transmission time assigned to the time synchronization message.
As a method for solving the above-described problem, there is the technology disclosed in JP 2012-199820A. JP 2012-199820A discloses a method in which a plurality of transmission times are predicted in an upper layer in advance, a plurality of secure time synchronization messages to which each of the predicted transmission times is assigned are prepared, and when a time synchronization message is actually transmitted in a physical layer, a time synchronization message to which a predicted transmission time having the minimum difference from the actual transmission time is assigned is selected and transmitted.